1. Field of the Invention
This invention relates to a rotary mimeographic transfer printing machine using a stencil.
2. Description of the Related Art
A typical conventional rotary mimeographic printing machine has a master drum for supporting a stencil on its outer circumferential surface. The master drum is rotatable and is equipped with an ink supply means inside the drum. A pressure roller is situated adjacent to the master drum, and on both sides of the master drum and the pressure roller there are situated a sheet supply means and a sheet discharge means.
A printing sheet supplied from the sheet supply means is fed as clamped between the master drum and the pressure roller, which are rotatable in synchronism with each other. To the printing sheet, the ink forced through a perforated image of the stencil is transferred. Then the printed sheet is peeled from the master drum to enter the sheet discharge means.
For obtaining a clear printed image by such conventional rotary mimeographic printing machine, the amount of ink to be transferred to the printing sheet must be controlled suitably. The amount of ink to be transferred to a printing sheet depends on the mechanical adjustment of the mimeographic printing machine and the quality of the printing sheet.
Conventionally, for mechanical adjustment of the amount of ink to be transferred to a printing sheet, it has been customary to adjust the pressure given between the stencil and the printing sheet by the pressure roller or to adjust the amount of ink to be supplied to the inside circumferential surface of the master drum by the ink supply means.
By the foregoing mechanical means, however, it was difficult to adjust the amount of ink to be transferred. For example, if the amount of ink to be transferred is reduced as the result of adjustment of the printing machine, the amount of ink transferred would be inadequate locally in the printed image which results in a blurred and hence unclear print. Yet if the amount of such ink could be increased in an attempt to improve this problem, such excessive ink would run on the printing paper. Besides, ink on a preceding printed sheet would tend to transfer to the back surface of a succeeding printed sheet,and on some occasions the image on the front surface of a printed sheet would be seen from the back side.
As mentioned above, the amount of ink to be transferred would be influenced also by the quality of a printing sheet, namely, the degree of ink absorption and/or smoothness of a printing sheet. In general, the smoother the printing sheet, the less the amount of ink will be transferred. Practically, however, there are an extremely wide variety of printing sheet qualities so that it is impossible to adjust the amount of ink, to be transferred based on the quality of the printing sheet. With the conventional rotary mimeographic printing machine, it is very difficult to provide a suitable amount of ink and to form a clear print image.